Visualization: 3 years of GPS-tracked running in the Bay Area

I've been using my Garmin Forerunner running watch for around 4 years now, 3 of which in the Bay Area. Tonight I exported all the data to Google Earth, and was surprised to see the resulting detail that came out of it. It turns out the error in the GPS signal essentially creates a heat map of my favourite runs, which I thought looks pretty cool.

He says on his blog post that he's going to try to find a way to display the same data with the date and time information display somehow, as well. What I don't understand, though, is where the error in the GPS signal is. This just looks like overlaid routes to me! Tim?

21 responses to “Visualization: 3 years of GPS-tracked running in the Bay Area”

I think he means how thick the lines are along his most frequented routes. The thickness probably isn’t because his path wandered 50 feet left or right as he ran, but because the GPS triangulation varied by that amount each time he traversed the route.

Yeah, MAPPO (nice name!) is right. If it hadn’t had this variation, then the most frequently travelled routes wouldn’t have been any thicker, and he’d have had to use some software to get the effect that this gave him for free.

The error refered to is the fact that the GPS doesn’t ‘know’ exactly where you are, but instead can plot your location to within a few metres.

If there was no error (uncertanty, actually) then each time he ran down the west side of a street, the GPS would plot his location exactly where he was, within a few inches. If this were to happen the repeated paths would overlap completely, and you’d never be able to see which routes were most often used.

As it is, because of the uncertanty, the GPS trace ‘wanders’ over the approximate path that was taken, as over time you get the ‘heat map’ effect.

Also, in theory, the places where the signal is weakest, or fewer sats were in view (tall buidings, many trees), would also show increased wandering, and you would get wider traces, even if the path was one not often travelled.

Notice the straight lines that cut across the city. Those represent times when he went from one location to the other when the GPS was off.

The line varies more than the runner themselves does, due to sattelite errors of 20 feet or so. So the places he runs more than once do not line up exactly as they are placed on the map, and thus those lines look thicker Of course there is the runners own variance as well. But if you have only run a route once, you are only going to have one thin line, rather than several fibers of tracking data.

Very cool, I’ve been going on a lot more walks now that I’m living in the city, and I’ve been thinking of getting an Amod AGL3080 to log where I go… It runs about $70, and has no display or anything of the sort, just stores raw data on inbuilt 128MB of memory which shows up on the computer as a mass storage device… Anyone ever used one of these or have any better alternatives in the same price range?

The overlay of many slightly wobbly traces which gives this its coolness is also used, in OpenStreetMap, to give the best track for a line: the road will run down the hottest part of the fuzzy heat map. It’s a sort of brute-force accuracy refinement, ‘cept it’s done by humans.

@timcederman: You linked to a model 101 that does not have download capability. The 201 model does (via serial as you indicated; though you can also probably use a USB to serial converter that I used on my old GPS units back in the day) and it costs $114. For $150 you can get the one, model 301, that does have a USB connection, does heart rate monitoring, and other stuff.